Chlamydia trachomatis is a sexually transmitted pathogen that is a principal cause of pelvic inflammatory disease and female reproductive failure (infertility and miscarriage). The immunopathology of C. trachomatis-associated reproductive failure is not completely known. Whereas active C. trachomatis infections of the lower genital tract are routinely diagnosed and treated, occult disease as evidenced by C. trachomatis DNA in the upper genital tract has only recently been described. We hypothesize that chronic subclinical disease as evidenced by persistent C. trachomatis in the endometrium of women causes reproductive failure by stimulating a local T Helper 1-cytokine mediated immune response. Cytokines associated with T Helper 1-immunity can disrupt reproductive function at several levels both before and after implantation. The overall objectives of this project are: 1) to determine the prevalence of occult C. trachomatis (chlamydial DNA) in the endometrium of women undergoing in vitro fertilization for tubal factor infertility and in women with a history of unexplained recurrent spontaneous abortion compared to women with successful reproductive histories; 2) to characterize local cellular immunity in the endometrium of these women; and 3) to correlate the presence of C. trachomatis DNA and parameters of T Helper 1-immunity with subsequent reproductive success and failure.